Computer programs are currently made extensible and efficient by the use of adjunct program modules such as plug-ins and dynamic link libraries. Plug-ins are computer program modules which can alter the behavior of a computer program without changing the computer program itself. A common example of plug-ins are those associated with currently ubiquitous web browsers. Briefly, a web browser is a computer program by which a user retrieves multimedia documents and information through that portion of the Internet known as the World Wide Web. Installation of plug ins allow modification of the behavior of the web browser without re-installing or otherwise changing the computer instructions of the web browser itself. One example of such extended functionality is the embedded display of images of the Tagged Image File Format (TIFF). Such functionality is not provided by some web browsers currently, but installation of certain plug-ins add that functionality. To use the plug-in, applications such as web browsers are designed to look for installed plug-ins and, if installed, invoke execution of those plug-ins upon activation of a particular function or activity.
Plug-ins can sometimes be implemented as dynamic link libraries. Dynamic link libraries can be used for other purposes as well. A dynamic link library is a collection of program modules which are generally not loaded until invoked by another program. The following example will illustrate. Consider a web browser which provides a spell-checking capability for forms data entry. A web browser is typically a resource-intensive program such that a considerable amount of memory is used when the web browser is executing A spell-checker can also be resource-intensive. By implementing the spell-checker as part of a dynamic link library, execution of the web browser does not immediately load the spell-checker into memory. Accordingly, the resources required for the spell-checker are not immediately consumed. Instead, the spell-checker is loaded for execution only when a user requests a spell checking function of the web browser. Such allows the web browser to execute more efficiently when the spell-check function is not invoked.
For reasons pertaining both to extensibility and efficiency, adjunct program modules such as plug-ins and modules of dynamic link libraries are quite popular. An additional factor in the popularity of such adjunct program modules is the simplicity with which they are implemented. To facilitate the use of adjunct processing modules, such modules are designed to be very easily identified and invoked. Virtually no safeguards are used to ensure only a specifically authorized computer program invokes execution of a particular adjunct program module.
The lack of security in adjunct program modules is a significant problem. The following example is illustrative. Consider that a computer user has collected a number of musical songs in the ubiquitous and renowned MP3 digital format and plays the songs on a computer using an MP3 player program. Consider further that the user has purchased and downloaded a number of songs in a secure, copy-protected format but wishes to play those songs along with the other songs in the MP3 format. The MP3 player program can be augmented with a plug-in adjunct program module to decode and play the secure, copy-protected format. Such an adjunct program module, when requested, can decode the secure, copy-protected music and produce un-secured, un-protected music for reproduction through the computer's sound logic and loudspeakers.
However, due to the accessibility of conventional adjunct program modules, any program could request decoding of the secure, copy-protected music data by the decoding adjunct program module. Accordingly, a cracker could write a simple program to request decoding from the adjunct program module and to re-write the decoded music in the MP3 format. The resulting MP3 music data file could have identical sound quality and could be distributed worldwide through the Internet without any encryption security or copy protection. Such would represent a catastrophic failure of the secure, copy-protected format decoded by the adjunct program module.
What is therefore needed is a security mechanism by which adjunct program modules can limit service to authorized program modules. Such would enable security-reliant computer processes to avail themselves of the benefits and advantages of adjunct program modules.